Pump diaphragm

ABSTRACT

A diaphragm for use in a fluid pump comprising a disc of resilient material having a substantially dished shape. The curvature of the disc is formed from a plurality of steps.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of and priority to Great Britain (GB) Application Serial No. 0716294.4, filed on Aug. 21, 2007, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to a diaphragm for use in a fluid pump, and more particularly, to a diaphragm configured to be coated with a protective layer such that the protective layer would avoid fracturing in use.

2. Background of Related Art

Diaphragm-type fluid pumps and, in particular liquid pumps, have a flexible pumping diaphragm which is driven to effect the pumping action of the pump. In such pumps, the diaphragm comprises a flexible circular or oval disc which has its outer peripheral edge clamped and sealed within the body of the pump. The diaphragm may have a central aperture which is secured to a moveable actuator such as a piston, which reciprocates back and forth causing the diaphragm to flex between a concave and a convex configuration. In an alternative pump configuration, however, the diaphragm does not have a central aperture and forms a partition with a driving fluid chamber in which the hydraulic pressure of the driving fluid is repeatedly alternated between high and low pressures, thereby causing the diaphragm to flex between a concave and a convex configuration. In both pump types, the repeated flexing of the pump diaphragm causes fluid displacement in a pumping chamber which results in the pumping action.

When such pumps are used to pump inert or un-reactive fluids, such as water, the diaphragm can be constructed from plain rubber material, since there is no problem with the fluid reacting with or corroding the diaphragm material. However, if the pump is intended for use with fluids having a more chemically reactive nature, an elastomeric diaphragm, such a natural rubber, alone is unsuitable as it is rapidly corroded, leading quickly to pump failure.

In order to solve this problem, it is desirable to provide the elastomeric diaphragm with a protective coating to prevent the pump fluid from reacting with or corroding the elastomer. However, the materials which would be most desirable to use for such a protective layer due to their excellent chemical resistance properties, such at PTFE, have plastic material properties, meaning they are unable to stretch and recover their original shape. However, when conventional pump diaphragms are in use, the repeated flexing between convex and concave positions causes the rubber of the diaphragm to repeatedly stretch and deform. Therefore, if a conventional diaphragm is coated with a protective layer, such as PTFE, it results in the protective coating cracking and splitting when the pump is in use, since the protective layer cannot cope with the repeated elastic deformation which the diaphragm experiences.

It is therefore an object of the present invention to provide a pump diaphragm that substantially alleviates or overcome the problems mentioned above.

SUMMARY

Accordingly, the present invention provides a diaphragm for use in a fluid pump comprising a disc of resilient material having a substantially dished shape, the curvature of the disc being formed from a plurality of steps.

Preferably, the diaphragm is circular, but may also be oval.

The plurality of steps are preferably formed from a series of flat annular rings of increasing diameter axially displaced from one another and joined at their adjacent edges by shoulder portions extending in an axial direction.

In a preferred embodiment, the diaphragm has a substantially inelastic chemically resistant coating on at least one side thereof. The chemically resistant coating may be formed on the concave side of the diaphragm or may be formed on the convex side, or may be formed on both/all sides of the diaphragm.

Preferably, the chemically resilient material is PTFE.

The resilient material may be rubber. However, if the diaphragm is for use in a hydraulic pressure type pump in which the diaphragm deflection is achieved by alternating hydraulic pressure of a driving fluid, then the resilient material will need to be compatible with the hydraulic media (e.g. oil). In such cases, the resilient material may be nitrile or a low-temperature resistant rubber material.

DETAILED DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic view of a prior art diaphragm pump;

FIG. 2 shows a series of cross-sectional views of a prior art pump diaphragm as used in the pump of FIG. 1;

FIG. 3 shows a perspective view of a pump diaphragm according to the present invention in its un-deflected natural state;

FIG. 4 shows a cross-sectional view along the line X-X shown in FIG. 3; and

FIG. 5 shows a cross-sectional view of the diaphragm of FIG. 4 in a deflected position.

DETAILED DESCRIPTION OF EMBODIMENTS

An example of a known diaphragm pump 10 is shown schematically in FIG. 1 and comprises a chamber 11, through which fluid being pumped flows, having an inlet 12 and an outlet 13. The inlet 12 includes a one-way valve 14 which allows fluid to flow into the chamber 11 though the inlet 12 but not out of the chamber 11 therethrough, and the outlet 13 includes a one-way valve 15 which allows fluid to flow out of the chamber 11 through the outlet 13 but not into the chamber 11 therethrough. A flexible diaphragm 16 is mounted in the wall of the chamber 11 separating the chamber 11 from a cavity 17. The diaphragm 16 is connected at its centre to a piston 18 of a pump driver 19. The piston 18 is driven backwards and forward in the direction shown by arrow ‘A’ to cause the diaphragm 16 to deform between position I in FIG. 1 where it extends into the cavity 17, and position II in FIG. 1, where it extends into the chamber 11. As discussed above, the prior art pump described here is of the type where the diaphragm deflection is actuated by a piston. However, alternative embodiments of prior art pumps use a driving fluid on the side of the diaphragm remote from the fluid being pumped, where the driving fluid pressure is alternated, which causes the diaphragm to flex. In such embodiments, the diaphragm clearly does not have the central aperture.

The fluid to be transported is caused to flow through the diaphragm pump chamber 11 by repeated reciprocation of the piston 18 between positions I and II. When the diaphragm 16 extends to position I, the volume of the chamber 11 is increased and the fluid pressure therein is reduced. This causes the fluid outside the chamber 11, which is unable to pass into the chamber 11 through the outlet one-way valve 15, to be drawn into the chamber 11 through the inlet 12 through the inlet one-way valve 14. Then, when the diaphragm 16 extends to position II, the volume of the chamber 11 is reduced and the fluid pressure therein is increased. Therefore, the fluid in the chamber 11, unable to pass through the inlet one-way valve 14, is forced out of the outlet 13 through the outlet one-way valve 15. As this cycle is repeated, the resulting repeated fluid displacement causes the fluid to be pumped through the diaphragm pump 10 from the inlet 12, through the chamber 11 and out of the outlet 13.

It will be appreciated that if the fluid being pumped is reactive or corrosive, then the diaphragm 16 will need to be provided with a protective layer interposed between the fluid and the rubber material of the body of the diaphragm 16, to prevent the diaphragm 16 from being corroded and causing the pump 10 to fail. It is important then, that this protective layer remains intact at all times to protect the rubber diaphragm 16 underneath. In the prior art pump shown, the diaphragm 16 deflects between positions I and II, and in doing so, the surface is stretched and compressed. This can be seen more clearly from FIG. 2 which shows the prior art diaphragm 16 in more detail in three positions, namely positions I and II at the most concave and convex positions in its range of motion, and also at a third position III, which is intermediate positions I and II where the diaphragm is deflected into a flat shape. The side of the diaphragm exposed to the fluid being pumped is on the concave side in FIG. 1. A reference distance between two radially-spaced points a,b on the concave side of the diaphragm in position I is shown as d1. As the diaphragm is forced to deflect to position III, the deformation of the diaphragm causes the distance between the same two reference points a,b to reduce to d2, as the surface of the diaphragm compresses. Then, as the diaphragm deflects further to position II, the distance between the same two reference points increases to d3 as the surface of the diaphragm stretches again. In this range of movement, the relationship between the distances is as follows:

d3>d1>d2

Therefore, if a protective layer is bonded to the diaphragm which has plastic properties, such as PTFE, the layer cannot cope with the repeated elastic stretching and compressing deformation that the diaphragm undergoes, and so the layer cracks. In use, these cracks would expose the rubber material of the diaphragm to the corrosive fluid being pumped, and so would cause the diaphragm to corrode and the pump to fail.

FIGS. 3-5 show a diaphragm 100 of the present invention for use in a pump such as that shown in FIG. 1, that does not suffer the drawbacks described above of known prior art pump diaphragms.

It can be seen that the diaphragm 100 is generally dish-shaped, as are known pump diaphragms, but its dish-shape is formed by a series of tiers or stepped layers 101 in the diaphragm material which are each displaced from one another in an axial direction of the central axis Y-Y of the diaphragm 100. Each layer 101 is formed as a flat annular ring, the rings increasing in diameter to form the tiers or steps, the inner peripheral edge 101 a and the outer peripheral edge 101 b of each ring being connected to the outer/inner peripheral edge 101 b, 101 a respectively of the adjacent ring 101 by shoulder portions 102 which extend in an axial direction.

The embodiment of the invention is shown having a chemically protective layer 103 of PTFE coated on the concave side of the diaphragm, seen more clearly in FIGS. 3-4. However, the pump could be configured such that the diaphragm is secured the other way round in the pump, in which case, the chemically protective layer would be coated on the convex side of the diaphragm, so that it is on the side in contact with the fluid being pumped.

The diaphragm 100 includes a central aperture 104 for a piston of a driver of a fluid pump to be secured thereto in a known manner, as schematically illustrated with the prior art device in FIG. 1.

As explained above in reference to FIGS. 1 and 2 of a prior art fluid pump and diaphragm, the diaphragm 100 of the present invention is repeatedly moved from its natural shape, shown in FIG. 4 to a deflected position, as shown in FIG. 5. In this repeated movement, the annular rings 101 do not stretch. Instead, they flex such that much of the deflection of the diaphragm 100 is effected at the annular rings 101. In addition, in the deformation of the diaphragm 100, the wall or shoulder portions 102 do not themselves bend or flex at all, but remain un-deformed. Therefore, the whole diaphragm 100 is able to repeatedly deflect between concave and convex positions without any part of its surface stretching to any significant degree. Therefore, the coating of PTFE 104 on the concave side (or convex side, in reversed diaphragm embodiments of the pump) of the diaphragm 100 in its natural position is not put under any strain to stretch during the repeated deflections and so the PTFE coating is not at any risk of cracking or fracturing in operation of a fluid pump having such a diaphragm 100 of the present invention.

The above embodiment is described having a protective coating of PTFE applied thereto. However, the scope of the invention is not limited to the diaphragm having a protective coating and includes an uncoated diaphragm of the configuration to accept such a coating without fracturing in use, as defined in claim 1. In addition, other protective coatings may be used in conjunction with the diaphragm of the present invention aside from PTFE.

Although a coating is shown on the concave side of the diaphragm, it may also be provided on both sides thereof to entirely coat the diaphragm, or may be provided on the opposite side thereof.

Although the embodiment of the diaphragm shown is circular, it may also be an oval disc shape within the scope of the claims.

The embodiment shown and described is for use in a fluid pump where the diaphragm flexing is actuated by a driving piston. However, the invention is not limited to such a diaphragm, and also covers diaphragms for use in hydraulically actuated fluid pumps, as described above. In such embodiments, the diaphragm would not have a central aperture 104.

Although the embodiment shown and described is configured with the diaphragm positioned with the concave side proximate the fluid being pumped, the invention is not limited to this configuration, and the diaphragm may be suitable for use with the convex side proximate the fluid being pumped, in which case, the protective coating would be provided at least on the convex side of the diaphragm. 

1. A diaphragm for use in a fluid pump comprising a disc of resilient material having a substantially dished shape, the curvature of the disc being formed from a plurality of steps.
 2. A diaphragm according to claim 1 wherein the plurality of steps are formed from a series of flat annular rings of increasing diameter axially displaced from one another and joined at their adjacent edges by shoulder portions extending in an axial direction.
 3. A diaphragm according to claim 1 having a substantially inelastic chemically resistant coating on at least one side thereof.
 4. A diaphragm according to claim 3 wherein the chemically resistant coating is formed on a concave side of the diaphragm when in its natural un-deflected state.
 5. A diaphragm according to claim 3 wherein the chemically resilient material is PTFE.
 6. A diaphragm according to claim 1 wherein the resilient material is an elastomeric material.
 7. A diaphragm according to claim 2 having a substantially inelastic chemically resistant coating on at least one side thereof.
 8. A diaphragm according to claim 4 wherein the chemically resilient material is PTFE.
 9. A diaphragm according to claim 2 wherein the resilient material is an elastomeric material.
 10. A diaphragm according to claim 1 wherein the disk is one of circular and oval in shape.
 11. A diaphragm for use in a fluid pump system, the diaphragm comprising: a plurality of annular rings, wherein each ring defines an inner annular edge and an outer annular edge, wherein the inner annular edge and the outer annular edge of adjacent rings are substantially axially aligned with one another; and an annular shoulder portion interconnecting adjacent annular rings to one another such that each annular ring is axially spaced from an adjacent annular ring, wherein at least the annular rings are elastomeric.
 12. A method of manufacturing a diaphragm comprising the steps of: collecting a plurality of flat annular rings of increasing diameter; axially displacing each ring from one another; joining the rings at their adjacent edges by shoulder portions in an axial direction; and coating a substantially inelastic chemically resilient material on at least one side thereof.
 13. The method of claim 12 wherein the resilient material is formed on the concave side of the diaphragm.
 14. The method of claim 12 wherein the resilient material is formed on the convex side of the diaphragm.
 15. The method of claim 12 wherein the resilient material is formed on both sides of the diaphragm.
 16. The method of claim 12 wherein the resilient material is an elastomeric material.
 17. The method of claim 12 wherein the resilient material is PTFE.
 18. The method of claim 12 wherein the resilient material is rubber.
 19. The method of claim 12 wherein the resilient material is a low-temperature resistant rubber material.
 20. The method of claim 12 wherein the resilient material is nitrile. 